1. Field of the Invention
The present invention relates to stabilizing agents permitting the preparation of suspensions of sodium silico-aluminates, also known as zeolites, having good stability in storage and during transport, and aqueous suspensions of sodium silico-aluminates containing such agents.
2. Description of the Background
Sodium silico-aluminates are increasingly used in formulations for detergent compositions to replace polyphosphates, which are responsible, upon being discharged into the natural environment, for the phenomenon of eutrophication affecting lakes and rivers.
Currently, to facilitate their use at the time of manufacturing detergent compositions, these zeolites are increasingly supplied in the form of aqueous suspensions containing approximately 50% of anhydrous zeolites, which are required to possess good stability in the course of storage and during transport.
For a long time now, those skilled in the art have proposed adjuvants enabling stable suspensions of zeolites to be obtained. FR Patent No. 2,287,504 and EP Patent No. 294,694, for example, describe the preparation of suspensions of zeolites stabilized with surfactants belonging, in particular, to the family of C.sub.16 -C.sub.18 fatty alcohols ethoxylated with 1 to 8 moles of ethylene oxide. This solution has the drawback of using very large quantities of stabilizing agent, on the order of 0.5 to 6% in relation to the suspension.
In FR Patent No. 2,512,690, the stabilizing agents mentioned are hydroxylated polymers obtained from starch, which prove efficient but which have to be used in large quantities, representing between 0.4 and 2.5% by weight and preferably between 1.4 and 1.5%, and which, in addition, because they are naturally biodegradable, necessitate the complementary addition of bactericides that are prejudicial to the environment at the time of discharge.
DE Patent No 3,021,295 describes a stable composition of zeolites containing 15% of nitrilotriacetic acid in salified form, a product the discharge of which is presently subject to strict regulations, and even prohibited in some countries.
FR Patents No. 2,455,479 and No. 2,461,516 claim as stabilizing agents polymers which have the drawback either of causing ammonia to be released in the highly alkaline medium (pH 10 to 13) of the zeolites in the case of FR Patent No. 2,455,479, or of failing to ensure good stability in the course of the preparation, storage and transport of the suspensions of zeolites at temperatures of between 50.degree. C. and 60.degree. C. (FR Patent No. 2,461,516).
Finally, JP Patent No. 61-101413 describes crosslinked styrene, sulfonated styrene and maleic anhydride based polymer compositions. These polymers are generally prepared in a solvent medium of the aromatic type, and such compositions will be difficult to obtain in a very pure state and pose the risk of them containing traces of solvent and styrene, a toxic monomer, which are sources of environmental pollution.
Thus, there, remains a need for agents, for stabilizing aqueous suspensions of sodium silico-aluminates, which do not suffer from the above-described drawbacks.